Anabinitiodetermination of the potentialhyphen;energy surfaces and rotationndash;vibration energy levels of methylene in the lowest triplet and singlet states and the singletndash;triplet splitting

摘要

The potentialhyphen;energy surfaces and rotationndash;vibration energy levels of the ground (Xtilde;thinsp;3B1) and first excited (atilde;thinsp;1A1) electronic states of the methylene radical have been determined by purelyabinitiomeans. The potentialhyphen;energy surfaces were determined by multireference configuration interaction calculations, using a fullhyphen;valence completehyphen;activehyphen;space reference space, with an atomichyphen;naturalhyphen;orbital basis set of size lsqb;5s4p3d2f1g/3s2p1drsqb;. The configuration interaction (CI) calculations were carried out at 45 points on the triplet surface and 24 points on the singlet surface. The Morse oscillator rigid bender internal dynamics (MORBID) procedure was used to calculate vibrational and rotational energy levels for12CH2,12CD2,13CH2, and12CHD. Also calculated were the zerohyphen;point vibrational energies, the singletndash;triplet splitting, and the dissociation energy. The zerohyphen;point energy of12CH2is found to be 127 cmminus;1(0.363 kcal/mol) greater in the triplet state than in the singlet. The singletndash;triplet splitting in12CH2is computed asT0=3116 cmminus;1(8.909 kcal/mol), compared with the experimentally derived value of 3156plusmn;5 cmminus;1(9.024plusmn;0.014 kcal/mol). The dissociation energy of the ground state is obtained asD0=179.06 kcal/mol, compared to an experimental value of 179.2plusmn;0.8 kcal/mol. The fundamental frequencies for the triplet state are obtained as ngr;1=3015, ngr;2=974, and ngr;3=3236 cmminus;1(the experimental value of ngr;2is 963.10 cmminus;1). The corresponding values for the singlet (experimental values in parentheses) are ngr;1=2787 (2806), ngr;2=1351 (1353), and ngr;3=2839 (2865) cmminus;1.